C51: On-Chip Banked PDATA Support

Information in this article applies to:

• C51

QUESTION

Some devices feature more than 512 bytes of on-chip RAM. The additional RAM (over and above the 128 bytes of data and 128 bytes of idata) is arranged both as xdata and banked pdata. Does the compiler support banked pdata memory?

ANSWER

The code overhead in implementing the bank switching, plus the risk that the wrong bank is selected during an interrupt routine or when using an RTOS is too great. The performance difference between using the extra RAM as xdata rather than pdata is minimal, so it would be much more efficient to use the memory as xdata rather than banked pdata.

If you only need 256 bytes of extra RAM, then reference the memory as pdata, otherwise reference it as xdata.

MORE INFORMATION

• C51: NXP/Philips 87C51RC 512-byte Internal RAM Support
• C51: Using Microcontrollers With On-chip XDATA
• C51: Philips P8XC557E8 Internal AUX-RAM Support

Last Reviewed: Thursday, February 25, 2021